Greenhouse Accessories Worth Buying

The cheapest accessory that changes decisions: it tells you the overnight low and the midday high, not the temperature at the moment you happened to look.

Every greenhouse decision -- when to sow, when to vent, whether you need a heater, whether the frost cloth is doing anything -- depends on a number most owners never measure: the overnight low inside the structure.

A min/max thermometer records the high and low since you last reset it, so a morning glance tells you what happened while you slept. That turns guessing into knowing, for the price of a bag of compost.

Hang it at plant height and out of direct sun. A thermometer in a sunbeam reports the sunbeam, not the greenhouse.

Skip it if: nothing. If you own a greenhouse and not one of these, you are guessing about the only variable that matters.

A greenhouse is measured in shelf area, not floor area, and staging is the cheapest way to double what you have.

The first thing most new greenhouse owners discover is that a 6 x 8 footprint is smaller than it looked in the listing. Staging is the fix: three tiers of trays in the floor space of one.

Look for slatted or mesh tops rather than solid ones. Water has to drain and air has to move, or the trays on the shelf become the place fungus gnats and damping-off start.

Plan for the seasonal switch. Staging is right in February and March when the greenhouse is full of seed trays, and comes out in May when tall crops go in and the shelves would only shade them.

Skip it if: you are growing tall crops to maturity in the ground inside. Staging and mature tomatoes compete for the same light.

Germination is driven by soil temperature, not air temperature -- and a heat mat is the difference between peppers in ten days and peppers in four weeks.

Seeds respond to the temperature of the medium they are in, not the room. Peppers and eggplants want soil in the 80s Fahrenheit to germinate briskly, and a 68-degree house gives them soil in the low 60s -- which is why they sit there for weeks.

A mat under the tray fixes that. Pair it with a thermostat probe if you can: without one the mat simply runs at its own output, which can be too warm for some seeds and is impossible to tune.

Take the tray off the mat once germination is done. Bottom heat after that encourages soft, stretched growth, and it dries the tray faster than you will remember to water it.

Skip it if: you only start cool-season crops. Lettuce, brassicas and peas germinate fine at room temperature and can actually be inhibited by heat.

The fix for the most common seed-starting failure. A windowsill grows pale, stretched seedlings; a strip light 3 inches above them does not.

A seedling stretches toward light. On a windowsill in February the light comes from one side and there is not enough of it, so the stem elongates, the plant gets pale and floppy, and it never fully recovers. That is the single most common seed-starting failure and it is entirely a light problem.

LED strips fix it because they can sit 2 to 4 inches above the leaves without cooking them. Distance is what matters more than wattage: the same light at 18 inches does very little.

Run them about 14 to 16 hours a day on a timer and raise them as the seedlings grow. Linkable strips mean a whole shelving rack runs from one outlet.

Skip it if: you have a genuinely bright greenhouse and are sowing in season. Then you are buying light you already have.